Popliteal artery entrapment syndrome (PAES) is a rare vascular disorder characterized by the compression of the popliteal artery (PA) behind the knee, primarily affecting physically active individuals. Entrapment may result from anomalous anatomy in the muscles and tendons surrounding the PA, such as the medial head of the gastrocnemius muscle or other structures, leading to arterial compression and potential injury. In contrast, functional PAES can also occur due to transient compression or occlusion of PA during specific movements or activities in the absence of anatomical anomalies. The precise prevalence of PAES is not well established; however, Bouhoutsos and Daskalakis [1] reported an incidence of 0.165% in young men entering Greek military service, and Gibson et al. [2] revealed a prevalence of 3.5% in cadaver specimens. Nonetheless, it has become evident that the condition is substantially more common than previously believed [3].

PAES can manifest with varying clinical signs and symptoms, depending on the severity, duration, and associated complications of arterial compression. The most common clinical manifestation is claudication due to PA stenosis or occlusion, followed by acute limb ischemia resulting from acute occlusion or distal embolization [4]. In some cases, a popliteal artery aneurysm (PAA) can develop due to post-stenotic dilatation or PA rupture, leading to the formation of a pseudoaneurysm.

In this report, we present a case of PAES with a PA pseudoaneurysm, with a focus on the differential diagnosis and importance of clinical suspicion of PAES in young patients with PAA. This study received approval from the Institutional Review Board (IRB) of Kyungpook National University Hospital (IRB no. 2023-08-011), and the requirement for informed consent was waived by the IRB.

A 36-year-old man was referred due to a 1-week history of acute, debilitating pain in his left limb. The patient was healthy with no known comorbidities and was not taking any medications for chronic conditions. Physical examination findings revealed a pulsating mass with moderate tenderness in the left popliteal fossa, unlike the right side. However, the left ankle pulse was palpable during the examination. Computed tomographic angiography (CTA) and conventional angiography conducted at the referring hospital confirmed the presence of a PA pseudoaneurysm (Fig. 1) and an abnormally inserted medial head in the gastrocnemius muscle (Fig. 2A). The contralateral extremity exhibited no signs of entrapment and had a normal PA trajectory. Subsequent duplex ultrasonography and magnetic resonance imaging (MRI) also identified the PA pseudoaneurysm and the abnormal insertion of the medial head of the gastrocnemius muscle (Fig. 2B, C). Based on the CTA and MRI findings, it was determined that the popliteal vein ran alongside the PA and was also located medially to the medial head of the gastrocnemius muscle. Consequently, our case was diagnosed as type 5 PAES, according to the Whelan and Rich classification [5].

Figure 1. The initial computed tomographic angiography (CTA) of the patient. (A) Axial CTA imaging revealed a 38×40 mm popliteal artery (PA) pseudoaneurysm (arrow) at the left popliteal fossa. (B) A three-dimensional reconstruction image demonstrated a PA pseudoaneurysm (white arrow) and an abnormally medially located PA (black arrow) caused by PA entrapment syndrome (posterior view). (C) The conventional angiography also revealed a stenotic, medially located PA (black arrow) caused by the medial head of the gastrocnemius muscle and a pseudoaneurysm distal to the stenosis (white arrow).

Figure 2. Initial computed tomography (CT), duplex ultrasonography, and magnetic resonance image (MRI) of the patient. (A) Axial CT image demonstrated the normally located medial head of the gastrocnemius muscle on the right popliteal fossa (arrow); however, the medial head of the gastrocnemius muscle (dotted line) was located laterally to the popliteal artery (PA) and popliteal vein (PV) on the left leg. (B) Duplex ultrasonography showed a pseudoaneurysm of the left PA. (C) The axial T1 image of the MRI also demonstrated an abnormal location of the medial head of the gastrocnemius muscle (arrow).

Surgery was performed 1 day after admission. Through the posterior approach with an S-shaped incision, the medial head of the gastrocnemius muscle was identified. Thereafter, the PA, both proximal and distal to the pseudoaneurysm, was dissected and controlled using vessel loops. The medial head of the gastrocnemius muscle was divided at the insertion site into the medial condyle of the femur. The great saphenous vein (GSV) at the distal thigh was harvested for arterial flow reconstruction. The PA, including the pseudoaneurysm, was resected, followed by an interposition grafting using the harvested GSV in a reverse fashion (Fig. 3).

Figure 3. (A) The operative photograph revealed the divided medial head of the gastrocnemius muscle (white arrow) and proximal anastomosis of the interposition graft with the great saphenous vein (black arrow). (B) The resected popliteal artery (PA) pseudoaneurysm measuring approximately 4.5 cm in diameter. The arrows indicate the proximal and distal ends of the resected PA.

The postoperative course was uneventful, and the ankle-brachial index of the left limb was 1.15 after the operation. Postoperative biopsy revealed thrombus formation without evidence of active vasculitis, and cultures of the thrombus within the aneurysmal sac revealed no microbial growth. After a smooth postoperative course, the patient was discharged 7 days after the operation. A CTA performed 1 month postoperatively revealed a patent interposition graft with a normal course (Fig. 4). During the 96-month follow-up with duplex ultrasonography surveillance, the patient remained asymptomatic, with no occlusion of the interposition graft or recurrence of the aneurysm.

Figure 4. One month after the operation, a three-dimensional reconstruction image of computed tomographic angiography revealed a patent interposition graft with the ordinary course (arrow) (posterior view).

The clinical manifestations of PAES can vary depending on factors such as chronicity, severity, and the extent of pathology. However, the most prevalent manifestation of PAES is claudication, which occurs due to stenosis or occlusion of the PA as a result of repeated traumatic interactions with the surrounding musculotendinous structures [4,6,7]. Moreover, in cases of functional entrapment, claudication may result from hypertrophy of the gastrocnemius muscle causing PA occlusion during contraction. This typically manifests as a sudden onset after exertion [8]. Conversely, the patient in this case had a 1-week history of acute-onset popliteal fossa pain, and the evaluation revealed a pseudoaneurysm associated with PAES. However, determining the exact mechanism underlying this pseudoaneurysm is challenging. Nonetheless, the abrupt rupture of a pre-existing post-stenotic dilatation or damaged PA without aneurysmal dilation could potentially lead to the formation of a pseudoaneurysm. Pseudoaneurysm formation is an exceedingly rare complication of PAES, with only a few reported cases to date [9-11]. In a study by Song et al. [11], endovascular treatment with self-expanding stent graft implantation in a patient with PAA and PAES was reported. A stent graft was used for treatment because PAES was not initially suspected as the cause of PAA. However, two weeks later, the stent graft became occluded. A careful re-evaluation of the preoperative CTA revealed that PAES was, in fact, the underlying cause of the PAA in this patient, and surgical revascularization was followed. Therefore, it is crucial to thoroughly evaluate preoperative imaging findings and maintain a high level of suspicion for PAES in relatively young patients with PAA to prevent inappropriate use of endovascular procedures.

Another noteworthy aspect in our case was the classification of PAES as type 5 according to the Whelan and Rich classification [5]. Anatomic PAES is categorized into types 1-5, resulting from aberrant embryological development of the PA, gastrocnemius muscle, or other myofascial structures within the popliteal fossa. Type 5 PAES represents any form of entrapment mechanisms involving or surrounding the popliteal vein as well as the PA. Conversely, functional PAES, classified as type 6, lacks anatomic abnormalities but is characterized by hypertrophy of the gastrocnemius, soleus, and/or plantaris muscles [6,8]. The frequency of anatomic PAES in the literature demonstrates that the most common anatomical variant is a type 2 anomaly, which involves a medial deviation of the PA resulting from a more laterally attached medial head of the gastrocnemius between the PA and the popliteal vein. This accounts for approximately 45%-74% of anatomic PAES [12-14]. The frequency of PAES with popliteal vein involvement is approximately 10%-15% [15], and cases related to deep vein thrombosis and chronic venous insufficiency have been reported previously [15]. In our case, although the popliteal vein was also entrapped, as well as the PA, no gross abnormalities were observed in the preoperative images or during surgery. However, in young patients and those with deep vein thrombosis at the popliteal lesion but without specific risk factors, PAES should be considered a potential cause of deep vein thrombosis.

The surgical management of PAES varies based on the severity of popliteal arterial damage, the extent of the lesion, and patient symptoms. Simple myotomy or releasing the compressing fibrous band can be effective for patients without popliteal arterial damage. However, in advanced cases such as a chronic occlusive lesion, distal embolization due to PA thrombus, or aneurysmal changes, the main treatments involve surgical revascularization with or without myotomy and excision of the damaged artery. Surgical treatment for PAES is a standard approach, with reported primary patency at 5 years ranges 72%-96% [4,13,14,16]. Kim et al. [13] reported their experience with bypass surgery for advanced PAES featuring segmental arterial occlusion. In their study, all 22 limbs underwent bypass surgery using a reversed saphenous vein, and the primary patency rates of the bypass graft were 80.9% and 74.6% at 1 and 5 years, respectively. Additionally, outcomes were better in patients with confined PA occlusion treated with a popliteal interposition graft using a reversed saphenous vein than in those treated with a longer bypass involving superficial femoral artery inflow. In our case, the patient underwent myotomy, segmental resection of the PA, including the PAA, and interposition grafting using a reversed GSV. The outcome was excellent, with no graft occlusion or symptom recurrence during the 96-month follow-up period.

In conclusion, we report a rare clinical presentation of a PA pseudoaneurysm in a patient with type 5 PAES. Although PAA is the most common peripheral arterial aneurysm associated with atherosclerosis in older patients, PAES should be considered as a causative factor in relatively young patients with PAA. Furthermore, myotomy, surgical resection of the PAA, and interposition grafting with the GSV can be employed in these patients and may yield optimal postoperative outcomes.

None.

Hyung-Kee Kim has been the editor-in-chief of the VSI since 2023. He was not involved in the review process. Otherwise, no potential conflict of interest relevant to this article was reported.

Conception and design: SH, HKK. Analysis and interpretation: all authors. Data collection: all authors. Writing the article: HJK, HKK. Critical revision of the article: SH, HKK. Final approval of the article: all authors. Statistical analysis: none. Obtained funding: none. Overall responsibility: HKK.